The present invention relates to the field of sunscreen compositions, i.e. compositions which, when applied to the skin, provide protection against the damaging effects of ultraviolet radiation. More particularly the invention relates to the field of sunscreen compositions which are formed as an oil in water emulsion.
In recent years, the general public has become more and more aware of the damaging effects of sunscreen compositions have become popular for people who spend time in the sun. Generally, such sunscreen compositions include active sunscreen agents, such as Padimate O, which absorb ultraviolet light in the erythemal region (280-320 nanometers), i.e. the region linked to erythema and skin cancer. Those compositions formulated for greater protection typically also include a sunscreen agent, such as oxybenzone, which absorbs ultraviolet light in a broader range (e.g. 280-340).
A challenge in formulating a sunscreen composition is to produce a composition with good substantivity, i.e. retention on the skin. Certainly, a sunscreen compositions effectiveness is tied directly to its ability to stay in place on the skin of the user for the entire time the user is in the sun. As a result, it is important that the composition be resistant to being rubbed off or washed off in water.
To make a sunscreen resistant to being washed off in water, i.e. waterproof, is particularly important in view of the fact that many consumers use sunscreen compositions in connection with water sports. Also, because sunscreen compositions are often used on hot days and/or in connection with strenuous physical activities, it is important that the compositions be waterproof so that it is not lost due to perspiration.
U.S. Pat. No. 4,663,157 to Brock describes an oil in water emulsion sunscreen composition which is reportedly resistant to rubbing off. The composition includes between about 1 and about 20 percent of a sunscreen agent, between about 0.25 and about 3 percent of a copolymer of ethylene and acrylic acid, between about 2 and about 10 percent emulsifier and between about 70 and about 96 percent water. The ratio of the sunscreen agent to the copolymer is stated to be between about 1:12 and about 15:1. This copolymer in this ratio is stated to improve the substantivity, particularly the resistance to rubbing off, of the composition.
U.S. Pat. No. 4,699,779 to Palinczar describes a sunscreen which is reported waterproof. The composition includes from about 15 to about 95 percent water, from about 1 to about 30 percent of an active sunscreen agent, from about 0.1 to about 6 percent ethylcellulose, from about 0.01 to about 12 percent surface active agent, and from about 0.03 to about 5 percent alkaline dispersion promoting agent.
U.S. Pat. No. 4,731,242 to Palinczar describes a sunscreen composition which is also reported to be waterproof. The disclosed composition includes from 15 to about 90 percent monhydric alcohols, from about 1 to about 30 percent of an active sunscreen agent, from about 0.1 to about 40 percent polyamide polymer, from about 0.1 to about 5 percent acrylic acid crosslinked polymer, and from about 0.1 to about 8 percent alkaline neutralizing agent.